import java.util.LinkedList;
import java.util.Queue;
public class Demo {
    static class TreeNode {
        public int val;
        public TreeNode left;
        public TreeNode right;
        TreeNode(int val){
            this.val=val;
        }
    }

    /**
     * 创建一棵二叉树 返回这棵树的根节点
     *
     * @return
     */
    public TreeNode createTree() {
        TreeNode node1=new TreeNode(1);
        TreeNode node2=new TreeNode(2);
        TreeNode node3=new TreeNode(3);
        TreeNode node4=new TreeNode(4);
        TreeNode node5=new TreeNode(5);
        TreeNode node6=new TreeNode(6);
        node1.left=node2;
        node1.right=node3;
        node2.left=node4;
        node2.right=node5;
        node4.left=node6;
        return node1;
    }

    // 前序遍历
    public void preOrder(TreeNode root) {
        if(root==null){
            return;
        }
        System.out.print(root.val+" ");
        preOrder(root.left);
        preOrder(root.right);
    }

    // 中序遍历
    public void inOrder(TreeNode root) {
        if(root==null){
            return;
        }
        inOrder(root.left);
        System.out.print(root.val+" ");
        inOrder(root.right);
    }

    // 后序遍历
    public void postOrder(TreeNode root) {
        if(root==null){
            return;
        }
        postOrder(root.left);
        postOrder(root.right);
        System.out.print(root.val+" ");
    }

    public static int nodeSize;
    /**
     * 获取树中节点的个数：遍历思路
     */
    public void size(TreeNode root) {
        if(root==null){
            return;
        }
        nodeSize++;
        size(root.left);
        size(root.right);
    }

    /**
     * 获取节点的个数：子问题的思路
     *
     * @param root
     * @return
     */
    public int size2(TreeNode root) {
        if(root==null){
            return 0;
        }
        int leftsize=size2(root.left);
        int rightsize=size2(root.right);
        return leftsize+rightsize+1;
    }


    /*
     获取叶子节点的个数：遍历思路
     */
    public static int leafsize = 0;
    public void getLeafNodeCount1(TreeNode root){
        if(root==null){
            return;
        }
        if(root.left==null&&root.right==null){
            leafsize++;
        }
        getLeafNodeCount1(root.left);
        getLeafNodeCount1(root.right);
    }

    /*
     获取叶子节点的个数：子问题
     */
    public int getLeafNodeCount2(TreeNode root) {
        if(root==null){
            return 0;
        }
        if(root.left==null&&root.right==null){
            return 1;
        }
        int leftsize=getLeafNodeCount2(root.left);
        int rightsize=getLeafNodeCount2(root.right);
        return leftsize+rightsize;
    }

    /*
    获取第K层节点的个数
     */
    public int getKLevelNodeCount(TreeNode root, int k) {
        if(root==null){
            return 0;
        }
        if(k==1){
            return 1;
        }
        int leftsize=getKLevelNodeCount(root.left,k-1);
        int rightsize=getKLevelNodeCount(root.right,k-1);
        return leftsize+rightsize;
    }

    /*
     获取二叉树的高度
     时间复杂度：O(N)
     */
    public int getHeight(TreeNode root) {
        if(root==null){
            return 0;
        }
        int leftheight=getHeight(root.left);
        int rightheight=getHeight(root.right);
        return leftheight>rightheight?(leftheight+1):(rightheight+1);
    }


    // 检测值为value的元素是否存在
    public TreeNode find(TreeNode root, int val) {
        if(root==null){
            return null;
        }
        if(root.val==val){
            return root;
        }
        TreeNode left1=find(root.left,val);
        if(left1!=null){
            return left1;
        }
        TreeNode right1=find(root.right,val);
        if(right1!=null){
            return right1;
        }
        return null;
    }

    //层序遍历
    public void levelOrder(TreeNode root) {
        if(root==null){
            return;
        }
        Queue<TreeNode> queue=new LinkedList<>();
        queue.offer(root);
        while(!queue.isEmpty()){
            TreeNode tmp=queue.poll();
            System.out.print(tmp.val+" ");
            if(tmp.left!=null){
                queue.offer(tmp.left);
            }
            if(tmp.right!=null) {
                queue.offer(tmp.right);
            }
        }
    }

    // 判断一棵树是不是完全二叉树
    public boolean isCompleteTree(TreeNode root) {
        if(root==null){
            return false;
        }
        Queue<TreeNode> queue=new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()){
            TreeNode tmp=queue.poll();
            if(tmp!=null){
                queue.offer(tmp.left);
                queue.offer(tmp.right);
            }else {
                break;
            }
        }
        while (!queue.isEmpty()){
            TreeNode tmp=queue.poll();
            if(tmp!=null){
                return false;
            }
        }
        return true;
    }
}
